The present invention relates to the field of horizontal directional drilling of boreholes, and in particular but not by way of limitation, to an apparatus and an associated method for generating power in the downhole end of a drill string used in near surface horizontal directional drilling.
A horizontal directional drilling machine is provided that acts on a drill string to form a borehole in the subterranean earth. The drill string has a fluid flow passage for the pumping of a pressurized fluid to the downhole end of the drill string to aid in the formation of the borehole. A generator assembly is disposed, at least in part, in the fluid flow passage and is responsive to the fluid flowing in the fluid flow passage to generate power to meet the downhole power requirements associated with horizontal directional drilling.
In one embodiment of the present invention the generator assembly has a housing supportable in the drill string so as to place a cavity formed within the housing in the fluid flow passage. An inlet in the housing directs the pressurized fluid into the cavity. An outlet is furthermore provided in the housing permitting an egress of fluid from the cavity.
An impeller is supported in the cavity for mechanical rotation in response to an impinging engagement of the pressurized fluid flowing from the inlet to the outlet. A generator is coupled to the impeller to convert the mechanical rotation to a power output.